Implement GraphQL API

Status

Proposed

Category

Frontend Development

Context

Our current REST API architecture is becoming increasingly complex as we add new features to the ShopFlow platform. We are experiencing several challenges:

Current API Challenges:

• Multiple API calls required to fetch related data (e.g., user profile + orders + shipping info)
• Over-fetching of data on mobile clients with limited bandwidth
• Under-fetching requiring additional API calls for missing information
• Version management complexity with multiple API versions
• Different API endpoints having inconsistent data formats
• Frontend teams struggling with API coordination and data fetching

Business Requirements:

• Improve mobile app performance by reducing data transfer
• Enable faster frontend development with flexible data fetching
• Reduce server load from unnecessary data transfers
• Provide real-time capabilities for order tracking and notifications
• Support for multiple client types (web, mobile, admin dashboard)

Proposed Solution:
We are considering implementing a GraphQL API layer alongside our existing REST APIs to address these challenges while maintaining backward compatibility.

Decision

We propose to implement a GraphQL API using Apollo Server that will serve as a unified data layer for our frontend applications.

Proposed Architecture

Implementation Plan

Phase 1: Foundation (4 weeks)

• Set up Apollo Server with basic schema
• Implement user and product queries
• Add authentication and authorization
• Set up DataLoader for efficient data fetching

Phase 2: Core Features (6 weeks)

• Add order and payment queries and mutations
• Implement real-time subscriptions for order updates
• Add comprehensive error handling
• Set up query complexity analysis and rate limiting

Phase 3: Optimization (4 weeks)

• Implement query caching with Redis
• Add monitoring and performance metrics
• Optimize N+1 query problems with DataLoader
• Add query cost analysis

Phase 4: Migration (8 weeks)

• Gradually migrate frontend applications to use GraphQL
• Maintain REST API compatibility
• Performance testing and optimization
• Documentation and developer tooling

Schema Design Principles

• Strongly typed: All data types clearly defined
• Nullable fields: Graceful handling of missing data
• Pagination: Cursor-based pagination for large datasets
• Versioning: Schema evolution without breaking changes
• Security: Field-level authorization and input validation

Consequences

Positive:

• Improved frontend development velocity with flexible data fetching
• Reduced network overhead and improved mobile performance
• Single endpoint for all data requirements
• Strong typing and introspection capabilities
• Real-time capabilities through subscriptions
• Better developer experience with GraphQL tooling
• Reduced over-fetching and under-fetching issues

Negative:

• Additional complexity in the backend architecture
• Learning curve for development team unfamiliar with GraphQL
• Query complexity can lead to performance issues if not monitored
• Caching strategies are more complex than REST
• Additional monitoring and debugging tools required
• Potential security risks with complex queries

Neutral:

• Need to maintain both GraphQL and REST APIs during transition
• Requires investment in new tooling and monitoring
• Team training and knowledge transfer required
• Migration timeline will impact feature development velocity
• Additional infrastructure costs for GraphQL server and caching

Implementation Considerations

• Backward Compatibility: REST APIs will remain available during transition
• Performance Monitoring: Implement query complexity analysis and timeouts
• Security: Add query depth limiting and rate limiting per operation
• Caching Strategy: Implement both query-level and field-level caching
• Error Handling: Consistent error format across all resolvers
• Documentation: Comprehensive schema documentation and examples

Success Metrics

Implementation Checklist

Phase 1: Foundation

• Research GraphQL best practices
• Evaluate Apollo Server vs alternatives
• Design initial schema structure
• Set up development environment
• Configure Apollo Server with authentication
• Implement basic user and product queries

Phase 2: Core Features

• Add order and payment queries/mutations
• Implement real-time subscriptions
• Add comprehensive error handling
• Set up query complexity analysis
• Configure rate limiting

Phase 3: Optimization

• Implement Redis query caching
• Add performance monitoring
• Optimize N+1 query problems
• Add query cost analysis

Phase 4: Migration

• Migrate web application
• Migrate mobile applications
• Performance testing
• Documentation and training

GraphQL Schema Example

type User {
  id: ID!
  email: String!
  profile: UserProfile
  orders(first: Int, after: String): OrderConnection!
  cart: Cart
}

type UserProfile {
  firstName: String!
  lastName: String!
  avatar: String
  preferences: UserPreferences!
}

type Order {
  id: ID!
  status: OrderStatus!
  items: [OrderItem!]!
  total: Money!
  createdAt: DateTime!
  shippingAddress: Address!
}

type Query {
  user(id: ID!): User
  product(id: ID!): Product
  orders(filters: OrderFilters): [Order!]!
}

type Mutation {
  addToCart(productId: ID!, quantity: Int!): Cart!
  updateProfile(input: UpdateProfileInput!): User!
  createOrder(input: CreateOrderInput!): Order!
}

type Subscription {
  orderStatusChanged(orderId: ID!): Order!
  cartUpdated(userId: ID!): Cart!
}

Performance Comparison

Note: These numbers are based on preliminary testing with simulated data.

REST API (Current)

• Average response time: ~150ms
• Average payload size: ~85KB
• Cache hit ratio: ~45%

GraphQL API (Projected)

• Average response time: ~95ms (37% improvement)
• Average payload size: ~42KB (51% reduction)
• Cache hit ratio: ~78% (73% improvement)

Related Decisions

• ADR-0003: Adopt Microservices Architecture - GraphQL will serve as a unified API layer over our microservices
• ADR-0005: Implement API Gateway Pattern - API Gateway will handle rate limiting strategies extended to GraphQL operations

Resources

External Links:

• GraphQL Best Practices
• Apollo Server Documentation

⚠️ Important: This ADR proposes a significant architectural enhancement that requires careful planning and phased implementation. ==Feedback from the Architecture Review Board is essential== before proceeding.

Last updated: December 2023